fix: try resolving conflicts by using getNewMappedName

[Norbiros]

Resolves architectury/architectury-loom#283

We’re seeing this conflict error:

Mapping source name conflicts detected:
  kn METHOD c ((Lkp;)Z) -> [kn/method_57832, kn/method_57826]
    fixable: replaced with method_57832
  kl METHOD c ((Lkp;)Z) -> [kl/method_57826, kn/method_57832]
  km METHOD c ((Lkp;)Z) -> [kn/method_57832, km/method_57826]
    fixable: replaced with method_57826
  kn$a$a METHOD c ((Lkp;)Z) -> [kn/method_57832, kn$a$a/method_57826]
    fixable: replaced with method_57832

The only unfixable conflict is:

kl METHOD c ((Lkp;)Z) -> [kl/method_57826, kn/method_57832]

It should prefer kl/method_57826, but currently doesn't.

This PR adds an alternative conflict resolution strategy: if all existing checks fail (e.g. parent-based), we fall back to resolving by member.cls.getName() + "/" + member.getNewMappedName().

This change is non-breaking and only runs as a last resort. It fixes the above issue without altering existing behaviour.